General Directorate of State Hydraulic Works, Ankara, Turkey. A. Ertunc. Engineering Faculty, Suleyman Demirel University, Isparta,. Turkey. Abstract The paper ...
Engineering properties of the magmatic rocks at the Pamukluk Dam site, Turkey S. Turkmen 7 E. Ozguler 7 A. Ertunc
Abstract The paper discusses the magmatic rocks that form the foundation material for the Pamukluk Dam, Tarsus, Turkey. The area has suffered extensive dyke intrusion and significant tectonic disturbance. The paper reports the results of both in situ tests and laboratory tests on block and borehole core samples. In general, the diorites and microdiorites have suffered little alteration and remained strong. The granophyres and less weathered acidic rocks are moderately strong while the gabbros are the weakest materials. The elastic moduli vary between 830 and more than 3500 MPa. Pressuremeter tests indicated that for a 120 m high dam, the settlement would vary between some 33 and 69 mm. Résumé L’article s’intéresse aux roches magmatiques qui constituent la fondation du barrage de Pamukluk, près de Tarsus (Turquie). La région a connu différents épisodes tectoniques, avec en particulier des sollicitations en distension, accompagnées d’intrusions filoniennes. L’article présente les résultats d’essais en place et d’essais en laboratoire sur des blocs rocheux et des échantillons de carottes de sondage. En général les diorites et microdiorites ont été peu altérées et ont gardé de bonnes caractéristiques mécaniques. Les granophyres et les roches acides les moins altérées présentent des caractéristiques moyennes, tandis que les gabbros sont les roches les moins résistantes. Les modules d’élasticité varient entre 830 et plus de 3500 MPa. Les essais de
Received: 3 August 1999 7 Accepted: 18 May 2000 S. Turkmen (Y) Department of Geological Engineering, Mersin University, Icel, Turkey e-mail: geo1st6panuk.cv.edu.tr E. Ozguler General Directorate of State Hydraulic Works, Ankara, Turkey A. Ertunc Engineering Faculty, Suleyman Demirel University, Isparta, Turkey
chargement à la plaque ont montré que pour un barrage de 120 m de hauteur, le tassement varierait entre 33 et 69 mm. Keywords Pamukluk Dam 7 Basic rocks 7 Pressuremeter tests 7 Settlement 7 Turkey Mots clés Barrage de Pamukluk 7 Roches basiques 7 Essais dilatométriques 7 Tassement 7 Turquie
Introduction Pamukluk Dam was designed to supply energy, irrigation and potable water to the area of Mersin City which is located 30 km north of Tarsus (Fig. 1). The dam is constructed on igneous rock. Samples obtained from drilled boreholes and adits have been examined petrographically and the behaviour of the rocks with different physical and mechanical properties defined. Plate loading tests were undertaken to define the elastic properties of the bedrock at the dam site in four exploratory adits, one on the right bank and three on the left bank of the river. The bearing capacity and permeability of the rocks have been determined using pressuremeter tests and water absorption tests respectively. The laboratory tests were carried out on block samples collected in the field and on core samples to define the physical and mechanical parameters of the basement materials.
Petrography of the magmatic rocks The bedrock at the dam site is formed of igneous rocks of Mesozoic age composed of acid and basic porphyry. These were intruded into volcanic rocks of different ages. The main mass consists of granitoid rocks which are generally altered. Some compositional variations have been observed within the boundaries of the other units. For example, granite can be observed 2 m away from the main boundary
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S. Turkmen 7 E. Ozguler 7 A. Ertunc
of the intrusion, although near the contact zone a transition of different rocks such as granodiorite, quartzdiorite and granophyre can be detected. The granite mass has intruded the magmatic complex. Subsequently it has been intersected with basic igneous dykes. Whilst in many areas the granite mass is the main material, in others it has been so intersected by dykes that it forms only a minor proportion of the material. From microscope studies, the rocks have been divided into acid, intermediate and basic material. In addition to the granites, monzonite, granodiorite, quartzdiorite, granite porphyry, granophyre, aplite and rhyolite have been recognised. As a result of tectonism, fractures and flexures can be observed. Within the granites, sericitisation, kaolinisation, chloritisation and epidotisation have been observed. Intermediate rocks (syenite and diorite) have been seen in the magmatic rock complex. Despite their strong and fresh appearance, these rocks were also affected by the tectonic stresses during which intense fracturing developed. Kaolinisation of both the feldspar within the syenites, particularly those that show perthitic texture, and the hornblendes has been identified as well as uralitisation and zeolitisation. Gabbro and diabase are the common basic rocks which are dominantly composed of anorthite and pyroxene minerals. In some cases, serpentinisation or locally iddingsitised olivine has also been observed. The gabbroic rocks have also been affected by the tectonic stress, with fractures passing through a number of minerals especially the pyroxenes. Similar alteration minerals to those found in the acidic and intermediate rocks were identified.
Geotechnical/engineering properties of the rock mass To investigate the effect of discontinuities and define the properties of the rock mass, observations were made of the different units forming the magmatic rock complex. The geotechnical characteristics of the discontinuities are
Fig. 1 Location map
Table 1 Geotechnical properties of rock discontinuities at dam site
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Rock name
Persistence (ISRM 1978)
Roughness
Aperture
Spacing
Rock quality designation (RQD)
Weathering of rock mass (ISRM 1978)
Slightly altered diorite Gabbro
Very low non-continuous Very low
Very rough
Closed
Closely jointed
50–75% (fair)
Rough, planar
Closed
Moderately jointed
50–75% (fair)
Granophyre
Very low
Rough, planar
Extremely tight
Closely jointed
Weathered gabbro and weathered granophyre Diabase
Very low
Slickensided
Closed
Moderately jointed
50–75% (fair) and 75–90% (good) 0–25% (very poor) and 25–50% (poor)
Slightly weathered rock Moderately weathered rock Slightly weathered rock Highly weathered rock
Very low
Smooth
Closed
Very closely jointed
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50–75% (fair)
Slightly weathered rock
Engineering properties, Pamukluk Dam, Turkey
presented in Table 1. The tests undertaken were those uities and hence recorded permeabilities in the order of defined by the Standard Institute of Turkey (TS 699, 1990) 10 –7 m/s (1–3 lugeons). and were carried out on both block samples and borehole Hardness cores. The hardness of the material was assessed using an N-type Schmidt Hammer to establish rebound numbers which Rock quality designation (RQD) The RQD of the cores was measured and the following were then correlated with those obtained on similar rocks. In this way an approximation of the uniaxial compressive results determined: strength was established while sc tests were also underDiorite taken in the laboratory. The results are provided in 20% of the material had RQDs of 0–25% (very poor) Table 2, which also gives the specific gravity, unit weight, 50% had RQDs of 50–75 (fair) water suction and apparent porosity. 30% had RQDs of 75–100 (good/very good) Gabbro Pressuremeter tests 10% had RQDs of 0–25% (very poor) Six pressuremeter tests (SK in Fig. 2) were undertaken to 20% had RQDs of 25–50 (poor) assess bearing capacity and possible settlement at the base 40% had RQDs of 50–75 (fair) of the dam. The pressure initially applied was equivalent to 30% had RQDs of 75–100 (good/very good) 1 atmosphere, increasing by 3 atmospheres for each 2 m Granophyre depth interval. Analysis of the test results indicated that for 10% had RQDs of 0–25% (very poor) a dam 100 m high and with a base width of 50 m, the 10% had RQDs of 25–50 (poor) settlement would range from 27 to 57 mm. For a height of 50% had RQDs of 50–75 (fair) 120 m, the settlement would be between 33 and 69 mm. 30% had RQDs of 75–100 (good/very good) The ultimate bearing capacity at the base of the dam was Altered gabbros and granophyres: calculated as ranging between 1.5 and 2.7 MPa. 50% had RQDs of 0–25% (very poor) 30% had RQDs of 25–50 (poor) Plate loading tests 20% had RQDs of 50–75 (fair) It can be seen that 30% of the diorite, gabbro and grano- The pressuremeter tests were supplemented by plate load phyre would be good quality rock mass as defined by tests to determine the elastic properties of the materials. Bieniawski (1989). The effect of the alteration is clearly Twenty-two horizontal plate loading tests (G in Fig. 2) evident, with 50% of the altered gabbro and granophyre were carried out in adits on the left-hand side of the valley rock mass being described as very poor quality rock and in order to define the deformation properties of the foundation rock. The total test time was 28 h 40 min, with none as good quality. pauses of 5 min at each load and unload stage and 25 min at each minimum and maximum pressure stage. The Permeability The results obtained from the water absorption tests have maximum load applied, between 3.5 and 7 MPa, was held revealed that the rocks in question have low permeability. for a period of 24 h to determine the deformation that the Packer tests were carried out at 2 m intervals. During these rock had suffered. tests, permeabilities in the order of 10 –6 to 10 –5 m/s It can be seen from Table 3 that G2 (the right-hand gallery) (10–20 lugeons) were recorded in the near-surface diorite has some lower values compared with those for the leftand gabbros located on the right-hand side of Pamukluk hand side of the valley, indicating a more altered and fracDam. Tests on the altered granophyre and gabbros indi- tured material. The strong, unaltered granophyres had cated that these rocks had very low permeability. With elastic moduli in the order of 3500 MPa; the strong but depth, however, the main rock mass had tighter discontin- slightly altered diorites, gabbros and granodiorites had Table 2 Index properties of magmatic rock complex at dam Samples
Gabbros Weathered gabbros Granophyres Diabases Diorites Weathered diorites Quartz diorites
Specific gravity
Unit weight (g/cm 3)
Water suction (%)
Apparent porosity (%)
Unconfined compressive strength (MPa)
Min
Max
Min
Max
Min
Max
Min
Max
Min
Max
2.70 2.70 2.80 2.84 2.88 2.82 2.66
2.77 2.75 2.82 2.86 3.00 2.87 2.68
2.31 2.43 1.89 2.75 2.66 2.50 2.46
2.60 2.69 2.60 2.77 2.95 2.64 2.55
1 2.8 1 1 0.4 3.4 2.8
5.4 4.3 4.2 1.4 1.1 6 4
1.7 7.6 1.9 3.5 1.2 8.6 6.9
11.7 10.5 10 3.9 4.8 15 8
12 5 13 25 45 8 15
60 10 48 30 125 32 30
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Fig. 2 Layout of boreholes and galleries at dam site
Conclusions
Examination of field samples has shown that the igneous rocks in the dam area consist mainly of gabbros, diorites, Table 3 Deformation measurements obtained in adits: G2 on right-hand granophyres and diabase. The tests carried out on block samples and drill cores showed that the elastic modulus side and G1, 3 and 4 on left-hand side of valley varied between 830 and 3500 MPa. Analysis of the plate loading tests indicated that the settlement for a 120 m high Adit Elastic Deformation Total Creep modulus modulus deformation factor dam would be in the order of 33–69 mm. Together with (MPa) (MPa) modulus (%) these data, water absorption test results of permeabilities (MPa) in the order of 10 –5 m/s near the ground surface decreasing to 10 –7 m/s at depth imply that this would be a good site G1 472–2544 155–1798 816–1545 0.7–22 for dam construction. G2 44–7197 105–3210 162–2622 12–53 G3 G4
127–10439 830–4174
579–7451 312–1438
408–4004 199–1040
17–38
References elastic moduli around 2500 MPa while the altered rocks Bieniawski ZT (1989) Engineering rock mass classification. had values of less than 2500 MPa. When the rocks are Wiley, New York, 251 pp severely fractured and altered, the elastic modulus value ISRM (1978) Suggested methods for the quantitative description decreases to some 830 MPa. of discontinuities in rock masses. Rock Mech Min Sci Geomech 15 : 319–368
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